Commentary Purg XVIII 49-60

The only 'substantial form' to be both distinct from matter and joined to it is the human soul, which is formed by pure divine intellect (as are the angels) and by emotional and vegetative powers (as are the beasts).  Its specifica vertute (defining disposition), as we learn at [Purg XVII 55-57], is composed of primal intellect and primal will, and is only perceptible in the action of the soul, not in itself.  Now, leaving intellection out of consideration, Virgil continues: We have no recollection or current understanding of our original inclination (to love God), yet we do demonstrate its presence in us, as the eagerness of bees for making honey reveals their 'defining disposition.'  This kind of (natural) will exists beyond and before moral assent.